The primary objective is to develop a continuous cardiac output monitor which can be easily and simply used in the clinical care of the critically ill patient. Intermediate goals are to verify (a) that the time-averaged cardiac output is inversely proportional to the integral of the impulse response of the right heart and proximal pulmonary artery, and (b) that this impulse response can be derived by a sufficiently long cross-correlation of a pseudo-randomly applied low power proximal heater source and the resultant distal temperature. Studies to date using computer simulations confirm that the average flow can be obtained by performing a cross-correlation of pseudo-random binary thermal input and resultant downstream temperature perturbation.